A superconducting magnet device that generates a high magnetic field using a superconducting coil in a superconducting state has conventionally been known. A superconducting magnet device generally includes a superconducting coil, a vacuum case housing the superconducting coil, an electrode member attached to the vacuum case, a conductive member (e.g., a copper wire) connecting the superconducting coil to the electrode member, and a refrigeration unit, mounted on the vacuum case, for cooling the superconducting coil. In such a superconducting magnet device, the superconducting coil is cooled by a refrigerator to a very low temperature whereas the electrode member attached to the vacuum case is kept under a room temperature (about 300 K). With the electrode member connected to the superconducting coil via the conductive member such as a copper wire, cold energy of the refrigerator is transferred to the electrode member via the conductive member, which may cause frost to grow on the electrode member. A technique for solving this problem is disclosed in JP 2009-277951 A.
In the technique disclosed in JP 2009-277951 A, a portion of a copper wire connecting a superconducting coil to an electrode pin is pushed against the inner face of a vacuum case to minimize growing of frost on the electrode pin. Cold energy of a refrigerator is transferred to the vacuum case via the copper wire before reaching the electrode pin. The cold energy transferred to the vacuum case is radiated from the vacuum case, and thereby growing of frost on the electrode pin caused by excessive cooling of the electrode pin is minimized.
The superconducting magnet device disclosed in JP 2009-277951 A preferably radiates further larger amount of cold energy transferred from the vacuum case. For a vacuum case made of stainless steel, frost might grow on the outer face of the vacuum case at a location opposite the portion onto which the copper wire is pushed, forming a shape corresponding to the portion.